The mechanism of axial rotation in the rat embryo: an experimental study in vitro

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Abstract
Axial rotation has been studied in 9- to 11-day rat embryos grown in culture by New’s watch-glass technique. Unlike the mouse, the rat embryo rotates towards its right side and rotation starts with the head end only. The twist then passes caudalwards until the whole axis has reversed its dorsoventral orientation and curvature. Contractions in cervical and cardiac regions appear to initiate the rotation. Posterior parts of 9- and 10-day embryos, isolated by transections at mid-trunk or cervical levels, show much less ability to rotate than unoperated controls: the frequencies of fully turned, partially turned and unturned embryos have been compared between control and experimental groups and show significant differences. There is more marked inhibition of rotation when the operation is performed at 9 days than at 10 days, and more with cervical than with mid-trunk transections. In all, 67 % of embryos transected at the mid-trunk level and 98 % transected at the cervical level were unable to rotate the posterior parts. Extrusion of embryos from the amniotic cavity also resulted in abnormal or incomplete axial rotation. The role of the membranes in facilitating rotation is discussed briefly.

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